The invention relates generally to particle beam systems, and more particularly to neutral beam systems.
In many applications, such as ion implantation or neutral beam injection into a fusion device, either positive or negative ion beams are employed. In either case, there are limitations in which either positive or negative ion beams will encounter some technical difficulties. In ion implantation, low energy (about 500 eV) B+ or P+ ion beams are needed for making shallow junctions. At such low energies, the transport of positive ion beams with reasonable currents are difficult because space charge force will cause the beam to blow up before it arrives at the target. One possible solution is to use a solenoid magnetic field to guide the low energy beam. Another possible solution is to employ plasma immersion ion implantation techniques. In either case, one has to make a radical change in implanter design.
In the case of high energy neutral beam injection in a fusion device, negative D− ions are normally employed. They are accelerated to energies higher than 500 keV and then neutralized before entering into the fusion device. Neutral beams are needed because the neutral particles can penetrate the strong confining magnetic field of fusion device without any deflection. The D− ions are extracted from an ion source and are accelerated to high energy by an electrostatic or radio-frequency acceleration system. The ions then pass through a gas or plasma neutralizer. For a gas neutralizer, less than 60% of the beam will be converted into neutral particles. The un-neutralized part of the beam will constitute a power loss.
Accordingly it is desirable to provide a neutral beam formation process and apparatus that reduces or eliminates the problems of beam blowup at low energy beam transport and the large amount of unneutralized beam in high energy beam formation.